Patent application title: METHOD FOR ASCERTAINING THE POSITION OF A MEDICAL INSTRUMENT IN A BODY

Abstract:

The present invention relates to a method for ascertaining the position of
the head of a medical instrument in a vascular system, wherein the
instrument can be inserted into the vascular system of a body and
describes a path at least partially inside the vascular system, and the
position of the instrument head is calculated from structural data,
length data and the relative position between a reference point and the
vascular system, wherein the instrument is guided past the reference
point, the structural data represents the structure of the vascular
system, and the length data represents the length of the path between the
reference point and the instrument head.

Claims:

1. A method for ascertaining the position of the head of a medical
instrument in a vascular system, wherein the instrument can be inserted
into the vascular system of a body and describes a path at least
partially inside the vascular system, and the position of the instrument
head is calculated from structural data, length data and the relative
position between a reference point and the vascular system, wherein the
instrument is guided past the reference point, the structural data
represents the structure of the vascular system, and the length data
represents the length of the path between the reference point and the
instrument head.

2. The method according to claim 1, wherein branch data, which represents
the branches which the instrument has followed in the vascular system
while inserted, is additionally incorporated into calculating the
position of the instrument head.

3. The method according to claim 1, wherein the length data is calculated
from a relative movement between the instrument and the reference point.

4. The method according to claim 3, wherein the relative movement is
ascertained by optical measurement.

5. The method according to claim 4, wherein the relative movement is
ascertained from a marking on the instrument.

6. A method for ascertaining the position of the head of a medical
instrument in a body, wherein the instrument can be inserted into the
body and describes a path at least partially inside the body, and the
position of the instrument head is calculated from course data, length
data and the relative position between a reference point and the body,
wherein the instrument is guided past the reference point, a relative
movement between the instrument and the reference point is automatically
ascertained, the length data is automatically calculated from the
relative movement, the course data represents the course of the path, and
the length data represents the length of the path between a reference
point and the instrument head.

7. The method according to claim 1, wherein a signal is generated when the
calculated position of the instrument head corresponds to a predetermined
position.

8. The method according to claim 1, wherein the actual position of the
instrument head is ascertained.

9. The method according to claim 8, wherein the reference point and/or the
length data are adapted from the actual position of the instrument head.

10. A program which, when it is loaded onto a data processing device or is
running on a data processing device, causes the data processing device to
perform the method according to claim 1.

11. A storage medium, on which the program according to claim 10 is
stored, or a signal wave which carries information constituting the
program according to claim 10.

12. A device for ascertaining the position of the head of a medical
instrument, comprising a computer on which the program according to claim
10 is running or is loaded.

13. An operation system comprising a medical instrument and a device
according to claim 12.

14. The operation system according to claim 13, comprising a camera in the
region of the instrument head for capturing a video image.

15. The operation system according to claim 13, comprising a device for
determining the actual position of the instrument head.

16. The operation system according to claim 13, comprising a camera which
is directed onto the body, for capturing an image from which the length
data can be ascertained.

Description:

RELATED APPLICATION DATA

[0001]This application claims the priority of U.S. Provisional Application
No. 61/094,894, filed on Sep. 6, 2008, which is hereby incorporated in
its entirety by reference.

FIELD OF THE INVENTION

[0002]The invention relates to: a method for ascertaining the position of
a head of a medical instrument in a body, in particular in a vascular
system; a program for performing the method; a storage medium on which
the program is stored; a device for ascertaining the position of the head
of a medical instrument in a body; and an operation system comprising a
medical instrument and such a device.

BACKGROUND OF THE INVENTION

[0003]In an operation or examination, medical instruments are often used
which are inserted into the body to be operated on, in particular into a
vascular system, wherein it is important to know the position of the
head, i.e. the inserted end, of the medical instrument.

[0004]In previous practice, the position has been determined using
real-time imaging by means of x-ray methods, wherein x-ray images are
continuously produced. However, this procedure incurs a radiation load
both for the patient and the physician.

[0005]Another approach, which is disclosed in the US patent application
2004/0171934 A1, is to use electromagnetic radiation generated at the
head of the instrument. To this end, a number of coils are employed which
firstly have to be integrated into the head of the instrument and
secondly have to be supplied with energy by the instrument. This can
necessitate a rather large instrument.

SUMMARY OF THE INVENTION

[0006]It is therefore the object of the present invention to provide a
method and device for ascertaining the position of the head of a medical
instrument in a body, in which a radiation load can be reduced and in
which in particular the overall size of the medical instrument does not
have to be increased. The latter enables a broader range of application
for the instrument.

[0007]This object is solved by the method, program, storage medium, device
and operation system specified in the independent claims. Advantageous
configurations may be gathered from the dependent patent claims.

[0008]One configuration of the invention relates to a method for
ascertaining the position of the head of a medical instrument in the
vascular system. The medical instrument can be inserted into a vascular
system of a body. When the instrument is inserted, it describes a path at
least partially inside the vascular system, wherein the instrument
penetrates into the vascular system at an entry point and follows the
course of the vascular system inside the body, wherein the course of the
vascular system determines the path which the instrument takes inside the
body. The position of the head of the instrument, referred to in the
following as the instrument head, is situated inside the vascular system.
The head is arranged at the inserted end of the instrument and for
example occupies up to 1, 10 or 25 percent of the length of the
instrument. If the instrument does not have a defined head, such as for
example a flexible tube or a needle, then the inserted end is designated
as the instrument head. The instrument is preferably flexible, for
example a catheter or endoscope.

[0009]The position of the instrument head is calculated from: structural
data which represents the structure of the vascular system; length data
which represents the length of the path between a reference point--which
the instrument is guided past--and the instrument head; and the relative
position between the reference point and the vascular system. This
relative position can for example be described by a position in a
reference frame in which a model of the vascular system lies. The
reference point preferably corresponds to the entry point of the
instrument in the body, but can also be any other point, inside or
outside the body, which lies on the path of the instrument. The path
reflects the shape of the instrument in its extension in the longitudinal
direction, for example the bend in a flexible tube-shaped instrument.

[0010]The length data accordingly describes the length of the part of the
instrument between the instrument head and the reference point. The
reference point advantageously lies inside the vascular system or at the
entry point of the instrument into the vascular system. The structural
data contains the three-dimensional configuration of the vascular system
and are preferably ascertained before the instrument is inserted into the
vascular system, for example as an angiogram using x-ray irradiation,
magnetic resonance tomography or computer tomography. The relative
position between the reference point and the vascular system establishes
a three-dimensional relationship by rendering the position of the
reference point relative to the vascular system. It is either known
beforehand or is ascertained and/or measured. One way is to mark the
reference point in the structural data manually, for example before,
during or after the instrument is inserted. Another way is to measure the
position of the body (and therefore the vascular system) and the
reference point with the aid of marker devices, such as are described
below.

[0011]If the relative position between the reference point and the
vascular system, the structure of the vascular system (for example as a
model) and the length of the path between the reference point and the
instrument head are known, then a finite number of positions at which the
instrument head can be situated exist inside the vascular system. The
actual position is dependent on the path which the instrument describes
in the vascular system. This path is usually planned before the
instrument is inserted into the body, such that this results in the
position--of the number of possible positions--which corresponds to the
actual position of the instrument head in the vascular system. The
calculated position of the instrument head can be used by the physician,
in particular when navigating the instrument. The physician can in
particular use the calculated position during the inserting process, in
order to check whether the planned path matches the actual path which
currently obtains. How the calculated position can be used to this end is
illustrated further below.

[0012]Branch data, which represents the branches which the instrument has
followed in the vascular system, is preferably additionally incorporated
into calculating the position of the instrument head. The branch data is
for example stored in a table which contains the path length at which
branching occurs, and in which direction. A second way is to mark the
branches in the structural data. If the branch data is taken into account
in the calculation, then it is for example possible to identify, from the
calculated position of the instrument head, whether the instrument is
following the path planned beforehand. The branch data can for example be
ascertained on video images recorded inside the vascular system, in the
region of the instrument head, while the instrument is being inserted.
Within the framework of this document, the term "video image" means both
static images and moving images. Alternatively, the branch data can be
obtained from ultrasound images, x-ray images, magnetic resonance
tomography recordings and computer tomography recordings, or output
signals of a gyro sensor on the instrument head.

[0013]In a preferred embodiment of the invention, the length data is
calculated from a relative movement between the instrument and the
reference point, wherein the term "relative movement" refers to the
entirety of a distance traveled and a movement direction. If the
instrument has moved relative to the reference point by a certain path
length, then the instrument head has moved by precisely this path length,
deeper into the vascular system or out of the vascular system, wherein
the relative movement need not necessarily be measured directly at the
reference point itself, but can also be measured at another point, i.e.
indirectly. If, for example, the reference point is situated inside the
vascular system, the relative movement can also then be ascertained
between the instrument and for example the entry point of the instrument
into the body, and equated with the relative movement between the
instrument and the reference point, for it may be assumed that the
relative movement between the instrument and the entry point is equal to
the relative movement between the instrument and any other position along
the path, i.e. also the reference point.

[0014]The relative movement is preferably ascertained by optical
measurement, in particular from a marking on the instrument. The marking
can for example be a barcode, a color code or a reflective marking. An
absolute length value can be encoded into the marking. The marking can
also be a regular pattern, the relative movement of which in relation to
the reference point is accumulated to give the length of the path. A
combination of image detection and image processing is also possible,
such as is for example performed in the case of an optical computer
mouse.

[0015]As an alternative to or in addition to optical measurement, the
relative movement can also be ascertained by a mechanical measurement,
for example by means of a scroll wheel which rolls off on the instrument.

[0016]A second configuration of the present invention relates to a method
for ascertaining the position of a head of a medical instrument which can
be inserted into a body and which describes a path at least partially
inside the body. As compared to the first configuration, the path of the
instrument is not limited to following the structure of a vascular
system.

[0017]The position of the instrument head is calculated from: course data
which represents the course of the path; length data which represents the
length of the path between a reference point--which the instrument is
guided past--and the instrument head; and the relative position between
the reference point and the body, wherein a relative movement between the
instrument and the reference point is automatically ascertained, and the
length data is automatically calculated from the relative movement.

[0018]This configuration of the invention is particularly suitable for
rigid medical instruments such as for example biopsy needles or screws.
The path of a rigid medical instrument corresponds to a straight line and
is therefore known.

[0019]The designs described in the following can be applied to both the
first and second embodiment.

[0020]The position of the entry point--and therefore a possible reference
point relative to the body and/or vascular system--can be determined on
the basis of a marker device, for example a marker star, or individual
marker elements (arranged stationary with respect to each other). A
marker star is an object comprising three or more spatially arranged
spheres which are fixedly connected to each other. The spatial positions
of the spheres can be detected for example by means of a 3D camera. Since
the positions of the spheres relative to each other are known, both the
position and the orientation of the marker star and therefore the
position of an object marked using the marker star can be ascertained
from the positions of the spheres.

[0021]Such an object is for example a device for measuring the relative
position between the reference point and the vascular system and/or body.
This device is preferably placed on the body at the entry point of the
instrument. In particular, the relative position between the marker
device and the reference point is known, such that by detecting the
marker device, it is possible to determine the position of the reference
point, in particular relative to the path.

[0022]In one configuration of the invention, a signal is generated when
the calculated position of the instrument head corresponds to a
predetermined position. The predetermined position is for example the
desired end position of the instrument head, or a (possible) branch in
the vascular system. The signal is for example an indication signal or
warning signal to the physician, or a rinsing signal which triggers the
introduction of a rinsing liquid by the instrument, in order to enable a
video image to be recorded in the region of the instrument head.

[0023]In another development of the present invention, the actual
(current) position of the instrument head is ascertained. This is for
example achieved by means of imaging methods such as x-raying or computer
tomography or electromagnetically determining the position by means of
coils with current flowing through them, the field from which is
detected. The actual position is the position which the instrument head
is currently occupying in reality. The actual position is for example
ascertained when the calculated position corresponds to a critical
position, for example the desired end position of the instrument head or
a branch in the vascular system. Since the actual position is not
ascertained while the instrument is being inserted, or only rarely and at
greater intervals in time than when ascertaining the position in a purely
x-ray-based way, the radiation load both for the patient and for the
physician is significantly reduced, even when an x-ray method is used.

[0024]In a preferred embodiment of the invention, the reference point
and/or the length data are adapted with the aid of the actual position of
the instrument head. This is for example achieved by setting the actual
position of the instrument head as the reference point and setting the
path length (traveled by the instrument head) in the length data to zero.
This creates a new starting point for the method in accordance with the
invention, on which determining the position is subsequently based.

[0025]Alternatively or additionally, the length data can be modified. One
way is to replace the length data with theoretical length data. The
theoretical length data is the length data which would result in a match
between the calculated position and the actual position if the
calculation were based on it. This theoretical length data is then used
as a basis when the instrument subsequently moves, for example when the
length data is updated on the basis of a relative movement between the
reference point and the vascular system and/or body. A second way is to
calculate a scaling factor, by which the path length is multiplied. The
scaling factor is determined such that the calculated position would
correspond to the actual position if the calculation were based on the
path length multiplied by the scaling factor. The path length multiplied
by the scaling factor is incorporated into the length data when the
position is subsequently calculated.

[0026]The invention also relates to a program which, when it is loaded
onto a data processing device or is running on a data processing device,
causes the data processing device to perform the method described above.
The invention also relates to a storage medium, on which such a program
is stored, or to a signal wave which carries information constituting
such a program.

[0027]The invention also relates to a device for ascertaining the position
of the head of a medical instrument, comprising a computer on which the
program described above is running or is loaded.

[0028]The invention also relates to an operation system comprising a
medical instrument and a device as described above. In one configuration
of the invention, the operation system comprises a camera in the region
of the instrument head for capturing a video image. The video image shows
an interior view of the body and/or vascular system and can be used both
to detect the actual position of the instrument head and when navigating
the instrument, for example at branches of the vascular system. If, for
example, the video image shows a branch in the vascular system, but a
branch is not present at the calculated position of the instrument head,
then the path of the instrument does not correspond to the desired path.
Given the path length and the information that the instrument head is
situated at a branch, it is possible to ascertain a number of paths which
describe the instrument in the vascular system. From this number, the
physician can determine the actual (current) path of the instrument, for
example on the basis of the size and/or structure of the vessels in front
of and/or behind the branch.

[0029]A deviation between the actual position and the desired path also
exists when the video image does not show a branch, but the calculated
position of the instrument head is situated at a branch.

[0030]In another embodiment, the operation system comprises a device for
determining the actual position of the instrument head. This device is
for example an x-ray apparatus, a computer tomograph or an
electromagnetic position ascertaining system.

[0031]The operation system preferably comprises a camera which is directed
onto the body, for capturing an image from which the length data can be
ascertained. The camera is for example an infrared camera. An infrared
camera has the advantageous that its sensitivity lies in the non-visible
frequency spectrum, and there is no additional illumination in this
frequency range to distract the physician and the patient.

[0032]The length data can be ascertained from the image from the camera
for example by detecting a marking in the form of a barcode, a color code
or a reflective marking on the instrument, which in particular represents
a path length traveled. A marking can also be a marker star such as has
already been described above. The marker is then arranged on a part of
the instrument which is not inserted into the body. The camera is
accordingly situated outside the body and detects the marking on the
instrument. A marker can also be provided as a reference for marking the
entry point. It is then also for example possible to detect a torsion
between the instrument and the entry point.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]The present invention shall be illustrated in more detail on the
basis of an example embodiment.

[0034]FIG. 1 shows an operation system in accordance with the invention.

[0037]FIG. 1 schematically shows an operation system 1 comprising a
computational unit 2, a monitor 3 and a 3D infrared camera 4. A patient 5
to be examined is situated within the detection range of the camera 4
shown by broken lines.

[0038]FIG. 2 shows a part of the vascular system 10 of the patient 5 which
is situated below the skin 6. The vascular system 10 is to be examined at
a position Z by means of an endoscope 7. The endoscope 7 is inserted into
the vascular system 10, which lies directly below the skin 6, at an entry
point E. The structure, i.e. the three-dimensional configuration, of the
vascular system 10 has been ascertained, by means of a computer
tomograph, before the endoscope 7 is inserted. The planned path between
the entry point E and the target point Z is shown by a broken line.

[0039]A regular marking 8 is situated on the endoscope 7, in the form of
equidistant bars which are detected by a measuring device 9 at the entry
point E. Two light sources and two photodetectors are arranged in the
measuring device 9, using which it is possible to ascertain the direction
in which and the path length by which the endoscope 7 has been inserted
into or drawn out of the vascular system 10 relative to the measuring
device 9 and/or entry point E. To this end, the measuring device 9 is
connected to the computational unit 2.

[0040]The position of points, such as the reference point or the entry
point E, and the position and/or orientation of objects, such as the body
5 or the measuring device 9, can be measured using marker devices or a
pointer, or directly input into the computational unit 2. A pointer is a
device comprising a marker device. The pointer is held at a point to be
detected, and the position of the point is calculated from the position
of the marker device. The position of the marker device is ascertained
for example with the aid of the camera 4.

[0041]The entry point E initially serves as a reference point for
determining the position of the head 7a of the endoscope 7. The position
of the entry point E as compared to the patient 5 and therefore the
vascular system 10 is known to the computational unit 2, for example from
measurements. The position and/or orientation of the body 5 is determined
for example from the positions of characteristic points of the body 5,
so-called landmarks. Alternatively, a marker star is situated on the body
5. At the point in time shown in FIG. 2, the instrument head 7a has been
inserted into the vascular system 10 as far as the position T. On the
path between the entry point E and the position T, the endoscope 7 has
followed the branches left, right and left in the vascular system 10.

[0042]From the markings 8 on the endoscope 7, the measuring device 9 and
the computational unit 2 have calculated length data which represents the
length of the path between the entry point E and the position T of the
instrument head 7a. The computational unit 2 calculates the position of
the instrument head 7a inside the vascular system 10 from said length
data, together with the relative position between the reference point E
and the vascular system 10, and from structural data which represents the
structure of the vascular system 10. This position usually matches the
actual position of the instrument head to a sufficient level of accuracy.

[0043]FIG. 2 shows a scenario in which the calculated position B does not
exactly match the actual position T, since the path of the endoscope 7 in
the vascular system 10 does not always take the shortest possible route.
The actual position T is ascertained in a check measurement by means of
an x-ray apparatus (not shown) and compared by the computational unit 2
with the calculated position B. On the basis of the deviations between
the two positions, the actual position T is defined as a new reference
point. When subsequently calculating the position of the instrument head
7a, this new reference point T and the path length traveled by the
relative movement between the endoscope 7 and the new reference point are
assumed beyond the position T. Since the traveled relative movement
cannot be directly measured at the position T, the measurement is again
taken at the entry point E. In subsequent calculations, it is thus
assumed that the relative movement between the endoscope 7 and the entry
point E corresponds to the relative movement between the endoscope 7 and
the new reference point T.

[0044]If calculating the position reveals that the instrument head 7a is
situated just short of the target position Z, then the computational unit
2 for example generates a warning signal for the physician and/or a
rinsing signal which causes the operation system 1 to inject a rinsing
liquid into the vascular system 10, in order to enable a video image to
be recorded by a camera situated on the instrument head 7a.

[0045]Instead of an endoscope 7, the instrument can also be another
flexible medical instrument, for example a catheter. In contrast to the
position ascertaining methods from the prior art, the method in
accordance with the invention exhibits the advantage that the position of
the medical instrument is not continuously determined using x-ray
recordings, therefore exposing both the physician and the patient to a
radiation load, but rather an x-ray recording is only optionally used to
verify the calculated position of the instrument head.

[0046]In the example application according to FIG. 3, a biopsy needle 11
comprising a sample tip 11a has been inserted into the body of the
patient 5. To this end, an inserting device 13--a so-called guiding
tube--has been placed onto the skin 6 of the patient 5 at the entry point
E. The biopsy needle 11 can be guided linearly through the inserting
device 13. Optionally, a marker star 14 is fixedly connected to the
inserting device 13 and comprises three spatially arranged spheres. The
camera 4 detects the spatial positions of the spheres. On the basis of
the known arrangement of the spheres, it is possible to unambiguously
calculate the position and alignment of the inserting device 13 relative
to the body of the patient 5 from the 3D image from the camera 4, if the
position and orientation of the body 5 are also known. The latter are
determined for example with the aid of a marker star or the position of
landmarks.

[0047]When the rigid biopsy needle 11 is inserted into the body, the
testing tip 11a describes a linear path. The length of the path, i.e. the
penetration depth of the testing tip 11a relative to the skin 6, is
ascertained by the inserting device 13 on the basis of a barcode 12 on
the biopsy needle 11. The path length is calculated in the same way as in
the example application according to FIG. 2, by means of two light
sources and two photodetectors.

[0048]In an alternative to the embodiment shown, the relative movement
between the reference point E and the biopsy needle 11 is not determined
in the inserting device 13 but rather from the image from the camera 4
which detects the barcode 12 on the biopsy needle 11.

[0049]Computer program elements of the invention may be embodied in
hardware and/or software (including firmware, resident software,
micro-code, etc.). The computer program elements of the invention may
take the form of a computer program product which may be embodied by a
computer-usable or computer-readable storage medium comprising
computer-usable or computer-readable program instructions, "code" or a
"computer program" embodied in said medium for use by or in connection
with the instruction executing system. Within the context of this
application, a computer-usable or computer-readable medium may be any
medium which can contain, store, communicate, propagate or transport the
program for use by or in connection with the instruction executing
system, apparatus or device. The computer-usable or computer-readable
medium may for example be, but is not limited to, an electronic,
magnetic, optical, electromagnetic, infrared or semiconductor system,
apparatus, device or medium of propagation such as for example the
Internet. The computer-usable or computer-readable medium could even for
example be paper or another suitable medium on which the program is
printed, since the program could be electronically captured, for example
by optically scanning the paper or other suitable medium, and then
compiled, interpreted or otherwise processed in a suitable manner. The
computer program product and any software and/or hardware described here
form the various means for performing the functions of the invention in
the example embodiments.

[0050]Although the invention has been shown and described with respect to
one or more particular preferred embodiments, it is clear that equivalent
amendments or modifications will occur to the person skilled in the art
when reading and interpreting the text and enclosed drawings of this
specification. In particular with regard to the various functions
performed by the elements (components, assemblies, devices, compositions,
etc.) described above, the terms used to describe such elements
(including any reference to a "means") are intended, unless expressly
indicated otherwise, to correspond to any element which performs the
specified function of the element described, i.e. which is functionally
equivalent to it, even if it is not structurally equivalent to the
disclosed structure which performs the function in the example embodiment
or embodiments illustrated here. Moreover, while a particular feature of
the invention may have been described above with respect to only one or
some of the embodiments illustrated, such a feature may also be combined
with one or more other features of the other embodiments, in any way such
as may be desirable or advantageous for any given application of the
invention.